Fix FreeBSD (10.x) build after 7dc9ae43

Include sys/user.h for declaration of 'struct kinfo_proc'.
Add -lutil to qemu-ga link for kinfo_getproc.

Signed-off-by: Ed Maste <emaste@freebsd.org>
Message-id: 1479778365-11315-1-git-send-email-emaste@freebsd.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>